This patent of invention pertains to natural or synthetic agalmatolite containing narrow particle distribution range, which can be used as mineral load or titanium dioxide extender, or precipitated calcium carbonate or calcined kaolin in the manufacture of industrial, or architectural, or automotive, or printing or demarcation paints, as well as in the production of plastic, rubber and cellulose. More particularly, the advantage of using natural agalmatolite, whose particle distribution is controlled, is in the end appearance of the paint, maintaining the texture, silky luster, fineness, opacity, wet scrub resistance and whiteness.
Dispersion paints are coating materials, which are used for protection and optical embellishment of civil engineering structures. There are groups interested in protective paints for construction, as well as their performance characteristics.
The desire is to have walls coated with a silky sheen. The objective of the paints is to provide such an appearance. To guarantee that the paints have a minimum sheen, semi-sheen agents should be added to the paints, which very substantially supply the directional reflection of light.
Semi-sheen agents are classified as mineral loads and are characterized by special grain-size properties which contribute to reduce the silky luster of a painted surface. The reduction of the silky luster is caused by the appearance of a micro roughness on a painted surface, in which the dispersed light is increased and the directional reflection is reduced. The semi-sheen agents, widely used for dispersion paints are silicates and carbonates. These can be extracted from natural deposits or produced synthetically. The most common natural products in the application of semi-sheen paints are kaolin, agalmatolite, talc, quartz, dolomite and calcite. For the synthetics, there is zinc oxide, precipitated calcium carbonate and calcined kaolin.
Micro roughness may arise by various manners. In the case of paints, the binding agent creates a surface similar to that of human skin. This is the result of incorporating a quantity of particles coarser than the rest of the components, whereby presenting a rough and homogenous surface. In this sense, the size distribution of the grains of all the solid components promotes this effect. If there is an insufficient quantity of the coarse fraction, there will be an “islands effect”, which is characterized as individual grains projected like islands on a smooth, homogenous film. Low sheen grains in the structure in the shiny film can be detected by the naked eye.
U.S. Pat. No. 7,758,688 describes the process of producing calcined kaolin having a well-defined particle distribution, which impacts the optical properties of the paints, improving opacity, whiteness, silkiness, texture and luster control. This product is used as titanium dioxide extender.
In U.S. Pat. No. 7,611,575, the properties of the calcined kaolin for a particle distribution less than 10 μm show an improvement in opacity, whiteness, silkiness, texture and luster control, as well as the use thereof as titanium dioxide extender.
Generally, the particle size distribution has little influence on the optical properties of agalmatolite. The commercially known finer agalmatolite product has an average particle diameter of 12 μm and d98 of 35 μm. This particle distribution confers this agalmatolite a whiteness of 77%, yellowness of 4, contrast ratio 92%, L*93 and wet scrub resistance of 17.